Exhaust systems for marine engines generally include an exhaust manifold connected to the engine at each row (or “bank”) of engine cylinders, and a corresponding exhaust conduit coupled to the exhaust manifold for directing exhaust gases from the manifold to an exhaust outlet. In conventional exhaust systems, the exhaust conduit includes a catalytic converter assembly having a catalyst that removes harmful emissions from the exhaust gases before being expelled through the exhaust outlet.
Exhaust systems can experience extremely high temperatures during use. For example, the core temperature of a catalytic converter in a conventional exhaust system can reach upwards of 1,000 degrees Fahrenheit (° F.) or more. For safety purposes, the U.S. Coast Guard requires that exterior surface temperatures of marine engine exhaust systems be maintained below 200° F. Accordingly, components of conventional marine engine exhaust systems, including the catalytic converter assemblies, are often liquid-cooled to ensure safe and compliant operating temperatures.
Referring to FIGS. 2 and 3, a prior art marine engine exhaust system 100 is shown, as disclosed in U.S. patent application Ser. No. 15/194,002 fully incorporated by reference herein. The prior art marine engine exhaust system 100 is used with a “V-8” engine, having two banks of four cylinders arranged in a known V-configuration. The prior art marine engine exhaust system 100 includes first and second exhaust manifolds 102, each being made of cast iron and being coupled to a bank of cylinders (not shown) of the engine via threaded bolts 104. As such, each of the exhaust manifolds 102 includes four exhaust inlet ports 106, each aligned with and receiving hot exhaust gases G expelled from a respective cylinder of the engine.
The prior art marine engine exhaust system 100 further includes first and second riser conduits 108, a Y-pipe 110, and an exhaust outlet conduit 112. Each of the first and second riser conduits 108 includes a lower riser section 114 made of aluminum defining an inlet end portion of the riser conduit 108 coupled to a respective cast iron exhaust manifold 102 with a clamp 116; a catalytic converter assembly 118 extending generally vertically from the lower riser section 114; and an upper riser section 120 extending upwardly from the catalytic converter assembly 118 and turning downwardly toward the Y-pipe 110 and defining an outlet end portion of the riser conduit 108.
The Y-pipe 110 includes first and second inlet legs 122 coupled to the first and second riser conduits 108 with clamped hoses 124, and an outlet leg 126 coupled to the exhaust outlet conduit 112 with a clamp 128.
As shown by directional arrows G in FIGS. 2 and 3, exhaust gases G are expelled from the engine into the exhaust manifolds 102. Each exhaust manifold 102 combines the incoming exhaust gases G into a stream, and directs the stream into the lower riser section 114 of the respective riser conduit 108. The exhaust gases G turn upwardly within the lower riser sections 114 and are directed through the catalytic converter assemblies 118, which reduce toxic pollutants in the exhaust gases G. Upon exiting the upper ends of the catalytic converter assemblies 118, the streams of exhaust gases G are directed through the upper riser sections 120 and then into the Y-pipe 110, which combines the two streams of exhaust gases G into a single stream. The unified stream of exhaust gases G is then directed through the outlet leg 126 of the Y-pipe 110 and into the exhaust outlet conduit 112, which directs the exhaust gases G through an exhaust system outlet 130.
As shown in FIG. 3, each lower riser section 114 includes an inner tube 134 and an outer tube 136 surrounding and spaced radially outward from the inner tube 134. Likewise, each upper riser section 120 includes an inner tube 138 and an outer tube 140 surrounding and spaced radially outward from the inner tube 138. Similarly, each catalytic converter assembly 118 includes an inner can 142 that houses a catalyst element 144 and an outer can 146 surrounding and spaced radially outward from the inner can 142. Each catalytic converter assembly 118 also includes inlet and outlet cone portions 148, 150 that taper from an intermediate portion 152 having an enlarged diameter for accommodating the catalyst element 144. Each catalyst element 144 removes toxic pollutants from the exhaust gases G, as described above.
The inner and outer tubes 134, 136 of each lower riser section 114, the inner and outer cans 142, 146 of the catalytic converter assembly 118, and the inner and outer tubes 138, 140 of the upper riser section 120 collectively define a riser liquid cooling passage 154, and may be arranged concentrically. As shown in FIGS. 2 and 3, the riser liquid cooling passages 154 communicate with manifold liquid cooling passage 156 (shown in exhaust manifold 102 in FIG. 3) via a cooling hose 160. Each cooling hose 160 is coupled at an inlet end to a manifold fitting 162 arranged on an outlet end portion of the respective exhaust manifold 102 (see, e.g., exhaust manifold 102 in FIG. 2) and coupled at an outlet end to a riser fitting 164 arranged on an inlet end portion on the lower riser section 114 of the respective riser conduit 108 (see, e.g., riser conduit 108 in FIG. 2).
As shown by directional arrows L in FIGS. 2 and 3, cooling liquid L is directed into the cooling inlets 166 from an external source (not shown) and flows through the manifold liquid cooling passages 156 in a direction parallel to a flow of the exhaust gases G, without contacting the exhaust gases G. The cooling liquid L then flows through the cooling hoses 160 and into the riser liquid cooling passages 154 of the riser conduits 108. In each riser liquid cooling passage 154, the cooling liquid L flows through the lower riser section 114, upwardly through the catalytic converter assembly 118, and into the upper riser section 120. While in the riser liquid cooling passage 154, the cooling liquid L flows parallel to the exhaust gases G but is separated from the exhaust gases G by the inner tubes 134, 138 and the inner can 142. The cooling liquid L then enters into the Y-pipe 110 where it is combined with the exhaust gases G, as indicated by overlapping arrows G, L in FIG. 2. The combined flows of exhaust gases G and cooling liquid L pass downwardly through the outlet leg 126 of the Y-pipe 110 and into the outlet conduit 112, to be ejected together through the exhaust system outlet 130.
One disadvantage of the prior art marine engine exhaust system 100 is the number of pieces required. The greater number of joints or connections between parts, the greater the likelihood of a leak. The present invention reduces the number of parts or pieces, thereby reducing the number of joints or connections between parts. An additional benefit of the present invention is a reduction in the number of clamps required in the exhaust system. Thereby, the present invention reduces the chances of a leak at the location of one joints joined by clamps.
An additional disadvantage of the known exhaust system 100 shown in FIGS. 2 and 3 is the weight of the cast iron exhaust manifolds 102. The cast iron outlet flanges 146 of exhaust manifolds 102 contact the aluminum riser inlet flanges 144 and are maintained in such a position with clamps 116. Due to the high temperatures to which such flanges are subject, these flanges may move over time and potentially damage the clamps 116 and/or flanges themselves due to the different materials of the flanges 146, 144.
Accordingly, there is a need for improvements to known marine engine exhaust systems to address these and other shortcomings.